The present invention generally relates to recording and reproducing apparatus and, more particularly, to apparatus that is adapted to record and reproduce real time television signals, using digital techniques.
Recently, a computerized system for recording and playing back slides and other graphic images has been made available for broadcast station useage. The system provides the high reliability and quality of a digital computer system employing magnetic disc pack storage. Such a system is commercially available from Ampex Corporation of Redwood City, California, as the model ESS-1 system and is disclosed and claimed in the aforecited U.S. patent applications.
This system consists of a video signal processor which utilizes digital techniques to store video images on a computer disc memory and which assigns an address to each image to facilitate rapid access. Two or three computer disc drives are employed under control of a system controller including a microcomputer. Access to the system is through keyboard controls located at the electronics rack, or from remote access stations. As many as eight access stations may be incorporated in the system, each equipped with a keyboard terminal and alphanumeric readout
Up to 1500 slides or other graphic images may be stored on-line in the typical two-disc pack drive system for immediate access. On-line random access time is less than 100 milliseconds
There are two playback channels in the typical system, allowing simultaneous outputs from each on-line disc pack. The system will record color or monochrome images, and operates in four modes: record, play, sequence assembly, and sequence play.
While the aforecited prior art system provided electronic storage and playback of stills, and while it was possible to record and playback video frames at less than real time rates, to obtain a slow motion effect it would be desirable if the system could record and playback television video signals on a real time basis, i.e., 30 frames per second. This capability could have been provided in the prior system by multiplexing the video signals to and from two disc packs, simultaneously. However, this would be costly and would seriously impair the still graphic storage and replay capability of the system.
It would be desirable to employ only one disc pack for the real time television video recording and playback, thereby leaving the second disc drive and disc pack for still graphic storage and replay. However, this was not possible in the prior system because the magnetic recording tracks were circular, each at a predetermined radius from the center of the disc and the magnetic recording/playback transducers of standard computer disc drives could not move from one recording track to the next and maintain and/or achieve time base lock during one vertical interval of television video signal, i.e. 1.3 milliseconds.